The objective of this investigation is to determine if the biological systems which maintain pulmonary sterility are adversely affected by exposure to atmospheres containing the air pollutants--sulfur dioxide and sulfate particles, sulfur dioxide and nitrate particles or nitrogen dioxide and sulfate particles. A rodent model serves as the test system for determining the effect of these exposures on the ability of the murine pulmonary macrophages to kill inhaled bacteria. Previous studies have shown that air pollutant concentrations which impair bacterial killing within the rodent lung also impair bacterial killing within the human lung and, therefore, this experimental model is a useful surrogate for the human. The results of our investigations show that exposure to both sulfur dioxide and sulfates at concentrations five times those of the present air quality standards does not affect the ability of the rodent lung to kill inhaled bacteria. These findings offer additional evidence that the present air quality standards for sulfate and sulfur dioxide are protective of human health. Studies are in progress to determine the effect of exposure to atmospheres containing sulfur dioxide and nitrate particles and nitrogen dioxide and sulfate particles on murine antibacterial defenses.